1. Field of the Invention
The present invention relates generally to an object inspection systems, and more particularly to a new object inspection system of the type that takes the photo image of an object to be inspected by a photo image sensing device.
2. Description of the Prior Art
Inspection systems for very small objects that are transferred by such means as belt conveyers under the prior art normally conduct inspection by microscopic magnification of the inspected object. When the inspected object is very small, it is difficult to accurately detect whether or not the inspected object is transferred to a predetermined detecting position with high precision. Under the prior art, the arrival of the object to the predetermined detecting position is detected by a photo switch, proximity switch, etc. When the inspected object is very small, there are various points of inconvenience.
In order to overcome such inconveniences object position detection systems are proposed where photo sensors are installed on the monitor screen on which inspected objects are projected. Such systems will be now explained in reference to FIG. 1. In the system under the prior art shown on FIG. 1, 1 is a belt on which an object 2 to be inspected is transferred in the direction indicated by an arrow 3. At a predetermined position in connection with belt 1, a photo image sensing equipment such as a television camera or the like 4 is installed which photo magnifies the inspected object 2. 5 is a monitor screen of the photo image sensing system 4 on which, at a predetermined position, a photo sensor 6 is installed in order to detect the positioning of the inspected object 2. In FIG. 1, the hatched block is an image 7 of the inspected object 2 on the belt 1 that is projected on the black background of monitor screen 5. Object 2 moves on the monitor screen 5 in the direction indicated by an arrow 8 towards sensor 6. When image 7, for instance, overlaps sensor 6, sensor 6 generates a start signal which is supplied to an object inspection or recognition system 9 such as a computer or the like to conduct the specified inspection of the object 2. However, according to the shape and dimensions of the inspected object 2 or the position thereof on belt 1, for instance, when the image 7 of the inspected object 2 as shown on FIG. 1, is in the position shown by broken like block 10 and moves in the arrow direction 8 on monitor screen 5, image 10 does not overlap sensor 6. Therefore, the inspection system 9 does not start its inspection operation and hence inspection of the object 2 is not conducted. This type of problem can occur even though the sensor 6 is installed with due considerations to the scan direction of the television camera 4 and the transfer direction of the inspected object 2.
Further, from the functional standpoint of television camera 4, since the position detection of the inspected object 2 is at intervals of 16.7 miliseconds, the positioning detection shall inevitably vary or scatter within 16.7 miliseconds.
It is further noted that non action may also be caused by trouble in the monitor television receiver, or upon a decrease of brightness thereof. In addition, the monitor television receiver is constantly in motion so that its life may be shortened.